1. Field of the Invention
The present invention relates to polymer blends comprising
a) from 50 to 85% by weight of a copolymer of propylene (A) with 1-alkenes comprising from 20 to 80% by weight of a high molecular weight copolymer of propylene (I) containing from 2.0 to 7.0% by weight of copolymerized 1-alkene and having a viscosity of from 500 to 1200 ml/g and from 20 to 80% by weight of a low molecular weight copolymer of propylene (II) containing from 4.0 to 10.0% by weight of copolymerized 1-alkene and having a viscosity of from 200 to 450 ml/g, PA0 b) from 5 to 10% by weight of a polymer of ethylene (B) and PA0 c) from 10 to 40% by weight of a rubber-like copolymer of propylene and a 1-alkene (C) containing from 30 to 70% by weight of copolymerized 1-alkene, PA0 a) from 50 to 85% by weight of a copolymer of propylene (A) with 1-alkenes comprising from 20 to 80% by weight of a high molecular weight copolymer of propylene (I) containing from 2.0 to 7.0% by weight of copolymerized 1-alkene and having a viscosity of from 500 to 1200 ml/g and from 20 to 80% by weight of a low molecular weight copolymer of propylene (II) containing from 4.0 to 10.0% by weight of copolymerized 1-alkene and having a viscosity of from 200 to 450 ml/g, PA0 b) from 5 to 10% by weight of a polymer of ethylene (B) and PA0 c) from 10 to 40% by weight of a rubber-like copolymer of propylene and a 1-alkene (C) containing from 30 to 70% by weight of copolymerized 1-alkene, PA0 a) from 50 to 85% by weight, in particular from 60 to 85% by weight, of the copolymer (A), PA0 b) from 5 to 10% by weight, in particular from 5 to 7% by weight, of the polymer of ethylene (B) and PA0 c) from 10 to 40% by weight, in particular from 10 to 35% by weight, of the rubber-like copolymer of propylene and a 1-alkene (C), where the sum of the three polymers (A), (B) and (C) is always 100% by weight. PA0 a) a titanium-containing solid component comprising at least one halogen-containing magnesium compound and an electron donor, PA0 b) an aluminum compound and PA0 c) a further electron donor compound. PA0 a) in a first polymerization step at from 30 to 150.degree. C., a pressure of from 10 to 100 bar and an average residence time of from 0.5 to 6 hours in the presence of a Ziegler-Natta catalyst system comprising a titanium-containing solid component, an aluminum component and, if desired, a further electron donor compound, propylene and 1-alkene are polymerized with one another to give the high molecular weight copolymer of propylene (I) and then PA0 b) in a second polymerization step at from 30 to 150.degree. C., a pressure of from 10 to 100 bar and an average residence time of from 0.5 to 6 hours in the presence of the Ziegler-Natta catalyst system used in the first polymerization step, propylene and further i-alkene are polymerized onto the copolymer of propylene (I) from the first polymerization step, forming the low molecular weight copolymer of propylene (II), so that the high molecular weight copolymer of propylene (I) and the low molecular weight copolymer of propylene (II) together give the copolymer of propylene (A).
and having a melt flow index (MFI) at 230.degree. C. under a weight of 5 kg of from 0.1 to 5 g/10 min, a molecular weight distribution (M.sub.w /M.sub.n) of from 6 to 20 and a total 1-alkene content of from 4 to 15% by weight.
The present invention further relates to a process for preparing such polymer blends, also moldings, hollow bodies and stamping plates comprising the polymer blends of the present invention and also a process for producing die stamping plates.
2. Description of the Related Art
Thermoplastic polymers, for ex ample propylene polymers, can generally be readily processed to produce moldings or hollow bodies. In the production of die stamping plates, however, there are sometimes difficulties resulting from, inter alia, the fact that the stamping plates frequently become brittle after prolonged use.
DE-A 4019053 discloses homopolymers of propylene having a broad molecular weight distribution (M.sub.w /M.sub.n) which are suitable, in particular, for producing films and moldings. However, die stamping plates produced therefrom have a certain brittleness and a relatively rough surface, which restricts their practical use.
Furthermore, EP-A 573862 describes crystalline polymers of propylene which likewise have a broad molecular weight distribution (M.sub.w /M.sub.n). These polymers are prepared by gas-phase polymerization in the presence of Ziegler-Natta catalysts. However, the propylene polymers obtained in this way have a relatively unsatisfactory brittleness during further processing and are not completely homogeneous. The production of die stamping plates from such propylene polymers by means of a customary platen pressing process is virtually impossible since the viscosity of the melt obtained is not sufficient.